Steel for low-temperature service

ABSTRACT

A steel having excellent notch toughness, for service at low temperatures, which can be used in the normalized or hardened and tempered condition and which contains 0.4-0.13 percent Carbon, 0.15-0.30 percent Silicon, 0.30-0.90 percent Manganese, 8.50-9.50 percent Nickel, 0.020-0.060 percent Aluminum, 0.008-0.020 percent Nitrogen. Balance, Iron and incidental impurities.

United States Patent Kambayashi et al.

[151 3,656,02 [451 Apr. 1, 1972 STEEL FOR LOW-TEMPERATURE SERVICE Inventors: Akira Kambayashi; Shun-lchi Shimada,

both of Kawasaki, Japan Assignee: Nippon Kokan Kabushiki Kaisha,

Kawasaki-shi, Kanagawa-ken, Japan I Filed: June 17, 1970 Appl. No.: 47,155

Foreign Application Priority Data June 21, 1969 Japan ..44/48793 U.S. Cl. ..75/124, 75/123 B, 75/123 K, 148/36 Int. Cl ..C22c 39/02, C22c 39/36 Field of Search ..75/123 K, 123 L, 124, 123 B; 148/36, 39

[56] References Cited UNITED STATES PATENTS 3,444,011 5/1969 Nagashima 148/36 X 3,496,034 2/1970 Alger ..148/36 X Primary Examiner-L. Dewayne Rutledge Assistant Examiner-J. E. Legru Attorney-Flynn & Frishauf [5 7] ABSTRACT 12 Claims, No Drawings 1 STEEL FOR LOW-TEMPERATURE SERVICE This invention relates to a steel having excellent notch toughness at low temperatures and which can be used in the normalized or hardened and tempered conditions. More specifically, this invention relates to-a steel containing 0.04 0.13 percent C, 0.15 0.30 percent Si, 0.30 0.90 percent Mn, 8.50 9.50 percent Ni, 0.020 0.060 percent Al, 0.008 0.020 percent N and up to 0.010 percent phosphorus, up to 0.010% sulphur and the balance iron and incidental impurities.

Steels of the above type are known generally to the art as ASTMA 353-67a and 553-67 steels, but these known types are not generally suitable for low temperature use under severe conditions because of their low notch strength. There is, however, a great demand for low temperature service steels and in order to satisfy that demand efforts have been made to improve the properties of this general class of steels. It is, therefore, an object of the present invention to provide an improve steel of the general ASTMA 353-67a or 553-67 type having improved properties, particularly at low temperatures.

It has been found, by one aspect of the invention, that the objects of the invention can be achieved by restricting the chemical composition of the general class of steel to a preferred range far narrower than the general range and also by introducing critical amounts of aluminum and nitrogen into the steel so that a desired amount of aluminum nitride may be precipitated. The preferred steel may then be used in the normalized or hardened and tempered conditions.

The upper limit of the aluminum content is set at 0.060 per cent to avoid problems of inclusions and reduced purity of the steel. The lower limit is set at 0.02 percent because below this figure no useful deoxidation is achieved nor is the nitrogen completely taken up.

The nitrogen content is controlled between 0.020 percent and 0.008 percent. The upper limit being determined by the upper limit of the aluminum content and the lower limit being determined by the requirement for at least a minimum amount of aluminum nitride.

The invention will be described in more detail by reference to a specific example.

EXAMPLE A steel having a chemical composition as set out in Table I below, was rolled to a plate thickness of 15 mm. Two samples of the rolled steel were then normalized at 800 C and tempered at 575 C and another sample was heat treated by hardening at 800 C quenching in water and tempered at 575 C for 1 hour. Tensile and impact tests were carried out on both samples as set out in Table 11. The tensile testing was conducted at room temperature and the impact testing was conducted zit-196 C.

strengthening effect obtained from the precipitation of aluminum nitride,

The reduced carbon and manganese contents and the aluminum nitride precipitation also contribute to the improved impact or notch toughness shown in the sample.

What is claimed is:

l. A steel for low temperature service consisting essentially of 0.04 0.13 percent carbon, 0.15 0.30 percent silicon, 0.30 0.90 percent manganese, 8.50 9.50 percent nickel, 0.020 0.060 percent aluminum, 0.008 0.020 percent nitrogen, up to about 0.010 percent phosphorus, up to 0.010 percent sulphur and the balance iron and incidental impurities.

2. A steel as claimed in claim 1 having a tensile strength of 5 at least 72 Kg/mm and an impact strength of at least 24 Kgm/cm in the normalized and tempered condition.

3. A steel as claimed in claim 1 having a tensile strength of at least 71 Kg/mm and an impact strength of at least 28 Kgm/cm in the hardened and tempered condition.

4. A steel as claimed in claim 1 having a tensile strength of at least 74 Kg/mm and an impact strength of at least 30 Kgm/cm in the hardened and tempered condition.

5. A steel as claimed in claim 1 consisting essentially of 0.06 percent carbon, 0.21 percent silicon, 0.40 percent manganese, 0.010 percent phosphorus, 0.008 percent sulphur, 9.22 percent nickel, 0.045 percent aluminum, 0.0l3 percent nitrogen balance iron and incidental impurities.

6. A steel as claimed in claim 1 consisting essentially of 0.05 percent carbon, 0.18 percent silicon, 0.42 percent manganese, 0.011 percent phosphorus, 0.005 percent sulphur, 9.20 percent nickel, 0.043 percent aluminum, 0.015 percent nitrogen balance iron and incidental impurities.

7. A steel as claimed in claim 2 consisting essentially of 0.06 percent carbon, 0.21 percent silicon, 0.40 percent manganese, 0.010 percent phosphorus, 0.008 percent sulphur, 9.22 percent nickel, 0.045 percent aluminum, 0.013 percent nitrogen balance iron and incidental impurities.

8. A steel as claimed in claim 2 consisting essentially of 0.05 percent carbon, 0. 18 percent silicon, 0.42 percent manganese, 0.011 percent phosphorus, 0.005 percent sulphur, 9.20 percent nickel, 0.043 percent aluminum, 0.015 percent nitrogen balance iron and incidental impurities.

9. A steel as claimed in claim 3 consisting essentially of 0.06 percent carbon, 0.21 percent silicon, 0.40 percent manganese, 0.010 percent phosphorus, 0.008 percent sulphur, 9.22 percent nickel, 0.045 percent aluminum, 0.013 percent nitrogen balance iron and incidental impurities. 7

10. A steel as claimed in claim 3 consisting essentially of 0.05 percent carbon, 0.18 percent silicon, 0.42 percent manganese, 0.011 percent phosphorus, 0.005 percent sulphur, 9.20 percent nickel, 0.043 percent aluminum, 0.015 percent nitrogen balance iron and incidental impurities.

11. A steel as claimed in claim 4 consisting essentially of TABLE I I 55 0.06 percent carbon, 0.21 percent silicon, 0.40 percent manganese, 0.010 percent phosphorus, 0.008 percent sulphur, C Si P S M N 9.22 percent nickel, 0.045 percent aluminum, 0.013 percent Q06 0 40 0.010 (1008 22 [1045 M13 nitro en balance iron and incidental im urities Contents g P 1 3 42 w ll. 9 will? -1 As la slaimeqm am! s qns essemlally of TABLE II Tensile test Impact test Plate Tensile thickness Yield point strength Elongation vE 0 vii-196* gauge (mm.) Heat treatment (kg/mm?) (kgJmmfl) (percent) (kgmJcmfi) (kgrnJcmJ) 15 {Normalizing and tempering 56 72 39 24 12 Hardening and temperlng... 69 76 37 23 20 Normalizing and tempering. 54 71 39 28 15 Hardening and tempering-.. 67 74 38 28 NorE.* vE 0" denotes an impactxa lge at 0 gfv lfllz stands for Yr otch notched on test piece. E stands for energy.

From the above example, it will be seen that the steel of the present invention has comparable tensile properties to the known steels for use at low temperatures. The carbon and manganese contents have been reduced and the tensile 0.05 percent carbon, 0.18 percent silicon, 0.42 percent manganese, 0.011 percent phosphorus, 0.005 percent sulphur, 9.20 percent nickel, 0.043 percent aluminum, 0.015 percent nitrogen balance iron and incidental impurities.

strength characteristic has been maintained because of the 75 =r it t it 

2. A steel as claimed in claim 1 having a tensile strength of at least 72 Kg/mm2 and an impact strength of at least 24 Kgm/cm2 in the normalized and tempered condition.
 3. A steel as claimed in claim 1 having a tensile strength of at least 71 Kg/mm2 and an impact strength of at least 28 Kgm/cm2 in the hardened and tempered condition.
 4. A steel as claimed in claim 1 having a tensile strength of at least 74 Kg/mm2 and an impact strength of at least 30 Kgm/cm2 in the hardened and tempered condition.
 5. A steel as claimed in claim 1 consisting essentially of 0.06 percent carbon, 0.21 percent silicon, 0.40 percent manganese, 0.010 percent phosphorus, 0.008 percent sulphur, 9.22 percent nickel, 0.045 percent aluminum, 0.013 percent nitrogen balance iron and incidental impurities.
 6. A steel as claimed in claim 1 consisting essentially of 0.05 percent carbon, 0.18 percent silicon, 0.42 percent manganese, 0.011 percent phosphorus, 0.005 percent sulphur, 9.20 percent nickel, 0.043 percent aluminum, 0.015 percent nitrogen balance iron and incidental impurities.
 7. A steel as claimed in claim 2 consisting essentially of 0.06 percent carbon, 0.21 percent silicon, 0.40 percent manganese, 0.010 percent phosphorus, 0.008 percent sulphur, 9.22 percent nickel, 0.045 percent aluminum, 0.013 percent nitrogen balance iron and incidental impurities.
 8. A steel as claimed in claim 2 consisting essentially of 0.05 percent carbon, 0.18 percent silicon, 0.42 percent manganese, 0.011 percent phosphorus, 0.005 percent sulphur, 9.20 percent nickel, 0.043 percent aluminum, 0.015 percent nitrogen balance iron and incidental impurities.
 9. A steel as claimed in claim 3 consisting essentially of 0.06 percent carbon, 0.21 percent silicon, 0.40 percent manganese, 0.010 percent phosphorus, 0.008 percent sulphur, 9.22 percent nickel, 0.045 percent aluminum, 0.013 percent nitrogen balance iron and incidental impurities.
 10. A steel as claimed in claim 3 consisting essentially of 0.05 percent carbon, 0.18 percent silicon, 0.42 percent manganese, 0.011 percent phosphorus, 0.005 percent sulphur, 9.20 percent nickel, 0.043 percent aluminum, 0.015 percent nitrogen balance iron and incidental impurities.
 11. A steel as claimed in claim 4 consisting essentially of 0.06 percent carbon, 0.21 percent silicon, 0.40 percent manganese, 0.010 percent phosphorus, 0.008 percent sulphur, 9.22 percent nickel, 0.045 percent aluminum, 0.013 percent nitrogen balance iron and incidental impurities.
 12. A steel as claimed in claim 4 consisting essentially of 0.05 percent carbon, 0.18 percent silicon, 0.42 percent manganese, 0.011 percent phosphorus, 0.005 percent sulphur, 9.20 percent nickel, 0.043 percent aluminum, 0.015 percent nitrogen balance iron and incidental impurities. 